Cryptography

If you are using Spongy Castle (which is a repackage of Bouncy Castle for Android), and are coming across a java.lang.NoClassDefFoundError like below on Android 4.x, you should perhaps check if you multi-dex is properly setup. If you are using multi-dex, go through the documentation, and make sure it is properly setup. In one app, where I was getting this error, it turned out the <application> tag was missing an attribute: <?xml version="1.